If you are not being paid for a gig, you need to check whether you are protected by workplace insurance.
Working just for the experience, to build up a portfolio, see a festival for free or develop contacts in the industry is standard practice for young people trying to break into the arts sector.
But accepting no wages is one thing, missing out on insurance in the case of an accident is another. For volunteers and interns, whether you have that coverage will depend on where you are.